Scientists have watched and studied plants and animals in nature for years. By observing contaminated bacterial cultures and apes treating illnesses in the wild by using certain plants, and by studying the secretions from frog skin and bees, new compounds have been isolated and sometimes modified that can be used to inhibit the growth of microbes. These natural and semisynthetic molecules are called biological controls, therapeutic agents, competitive inhibitors, drugs, and numerous other names. By being selectively toxic, the compounds inhibit microbes and have limited damaging effect on host cells. The compounds are intended for the treatment of diseased patients through oral intake or injection, rarely used topically (on surface).

In the early 1900s, Paul Ehrlich recognized that certain dyes stained micro-organisms but not the animal cells. By using this concept of "selective toxicity," Ehrlich discovered that an arsenic-containing drug would inhibit Treponema (causative microbe of syphilis). He named the drug Salvarsan because it was a salvation against syphilis and contained arsenic. In 1935 Gerhard Domagk realized that a fabric red dye called Prontosil could be used to treat septecemia (gram positive bacteria like Streptococcus and Staphylococcus in the blood. The inhibitingd ingredient in protonsil was identified as sulfanilamide and was quickly used to treat wound infections during World War II.

In 1929 Alexander Fleming published a paper on a drug produced by the mold Peincillium. This drug was named penicillin and possessed anti-bacterial characteristics. The use of therapeutic drugs that interfered with metabolism of microbes had now begun; and motivated by the impending World War II, large scale production of antibiotics began; and infant mortality, fatality from infectious diseases, and soldiers' deaths from microbes were greatly reduced.

A group of drugs called sulfa drugs were produced. These drugs prevented microbes from making folic acid needed in nucleic acid and vitamin B production. Currently a drug called bactrim is used to treat urinary tract infections as well as Pneumocystis pneumonia common in AIDS patients. Another sulfa drugcalled gantrusin is used to treat vaginal infections.

A second group of drugs includes the anti-viral drugs. The pandemic HIV infections (AIDS) has introduced numerous new anti-viral drugs. Anti-viral drugs imitate the structure of nucleotides and compete for sites on replicating DNA. Most of these drugs stop the viral multiplication by preventing the virus from penetrating the host cell, transcription, and maturing. Interferon is an anti-viral protein produced by infected host cells, and initially interferon was predicted to be a drug with great use and promise. Other anti-viral drugs include acyclovir (purine compound used to treat herpes), ribavirin (quanine compound used in aerosol form to treat infections by RSV—respiratory syncytial virus), AZT or retrovir (thymine compound used to treat HIV), and amantadine used to prevent influenza-A infections especially in the elderly.

Since protozoa and yeast are eucaryotic, the drugs used to inhibit their growth are more likely to harm human tissues. Amphotericin (used to treat systemic infections) and Nystatin (topical or roal drug developed in New York State and used to treat Candida infections) are two antifungal drugs that imitate the lipids in cell membranes. Griseofulvin is used in extreme cases of athlete's foot; cycloheximide is used to inhibit mildew on golf course greens; and compounds like vitavax, captan, carboxin, subdue, banrot, and trueban are antifungal drugs used in agronomy and horticulture. Among the most familiar anti-protozoal drugs are quinine (control malaria caused by Plasmodium), metronidazole or Flagyl (used to treat Giardia, Entamoeba, and Trichomonas), and dihydroemitine (used to induce vomiting or emesis to remove the protozoan).

Drugs used to treat helminth (worm) infections are developed to destroy the worm. Drugs that simply stop reproduction are usually not successful. Drugs like niclosamide (destroys the scolex of tapeworm so worm can not remain attached) and pyrantel (paralyzes the muscles of intestinal roundworms). Following treatment with these anti-helminth drugs, the adult worms are removed with the feces.